Circuit breaker contact actuating mechanism



Feb- 21, 1956 P. L. TAYLOR ET AL CIRCUIT BREAKER CONTACT ACTUATING MECHANISM WITH SEPARABLEI CONNECTION TO on PUMP Filed April 24, 1955 2 Sheets-Sheet l Feb. 21. 1956 p TAYLOR ET AL 2,735,914

CIRCUIT BREAKER CONTACT ACTUATING MECHANISM WITH SEPARABLE CONNECTION To OIL PUMP Filed April 24, 1953 2 Sheets-Sheet 2 a g j 2g gag-4 lama/ X: gamma CIRCUIT BREAKER IGNTACT ACTUATING MECHANISM WITH SEPARABLE CONNEC- TION Ti) OIL PUMP Philip L. Taylor, Alrington, and Joseph M. Ramrath, Mattapan, Mass, assignors to Allis-Chalmers Manufao turing Company, Milwaukee, Wis.

Application April 24, 1953, Serial No. 350,868 9 Claims. (Cl. 200-150) This invention relates to circuit interrupter-s and more particularly to are extinguishing structures therefor.

More specifically this invention relates to a novel structure for eifecting the very rapid initiation, elongation and extinction of electric arcs drawn in circuit interrupters. This invention is applicable to the interruption of high voltage arcs such as those drawn in 287 kv. circuit but is also applicable on low voltage circuits.

Experience has demonstrated that a rapid lowering of the dielectric strength of an arc extinguishing fluid, such as oil, occurs after it impinges upon the arc stream. It is therefore desirable to eliminate such contaminated fluid as quickly as possible, and to subject the arc stream to the action of fresh fluid of high dielectric strength. The isolation or disconnection of a capacitance load by a circuit breaker in an alternating current system is subject to transient overvoltages, the magnitudes of which depend on the capacitance of the load, the voltage of the system, and the type of the circuit breaker. In isolating such a capacitance load, interruption at the first current zero in the arc of the leading current is readily effected at a relatively small contact separation. In one-half cycle after the first current zero, the voltage of the source has reversed to its crest value, and approximately double this voltage appears across the circuit breaker contacts as a circuit recovery voltage. Whether or not restriking of the arc occurs depends on several factors, such as the type of the circuit breaker, including the speed and the magnitude of the separation of its contacts, the magnitude of the circuit recovery voltage, and the leading kva. of the load.

These circuit conditions are diflicult if not impossible to control. Therefore, restriking in most breakers must be expected especially under severe operating conditions, and the circuit interrupting structures must operate efficiently under such conditions.

in accordance with this inventio a new and improved circuit interrupting structure is provided in which an arc interrupter is immersed in arc extinguishing fluid. The interrupter may comprise a pressure generating chamber, a pair of cooperating contacts arranged in the chamber and comprising a stationary arcing contact and a movable arcing contact, and a stud supported in and protruding through the chamber. A lever pivotally mounted between the ends thereof on the stud has the movable arcing contact arranged at one of its ends for reciprocal longitudinal motion. A cradle is pivotally mounted at the other end of the lever and is guided for reciprocal longitudinal motion. A push rod is provided for actuating the cradle and the lever in contact closing direction against a biasing means which is provided for actuating the lever and cradle in contact opening direction. Means are provided for detachably connecting the push rod to the cradle including plane cooperating surfaces of the push rod and of the cradle to cause the cradle to receive parallel displacement during movement of the cradle in engagement with the push rod. Upon movement of the push rod in contact opening direction the lever and cradle are actuated States Patent to contact opened position by their biasing means to sepa- 7 rate the arcing contacts. A piston may be arranged to operate at the same time or arranged to operate in a predetermined sequence with the movable contact and to force a flow of fluid under pressure adjacent the arcing contacts to extinguish the are drawn therebetween, the movable contact being opened independently of the movement of the piston. Further, valve means comprising a valve element coaxially arranged on one end of the stud outside of the chamber and biased toward the chamber may be provided to form a substantially fluid tight seal at the point of intersection of the chamber and the stud. The valve element provides an opening in the chamber to reduce the pressure in the chamber if it reaches a predetermined value.

It is, therefore, one object of this invention to provide a new and improved circuit breaker mechanism for establishing and lengthening an arc.

Another object of the present invention is to provide a new and improved circuit interrupting mechanism for establishing and lengthening an arc in a jet of fluid in which the contacts are opened independently of the movement of the piston of the fluid pump.

A further object of this invention is to provide a new and improved circuit interrupting mechanism for establishing and lengthening an arc within a pressure chamber which controls the operating values of pressure within the chamber.

A still further object of this invention is to provide a new and improved circuit breaker mechanism for establishing and lengthening an are which subjects the arc to un-ionized arc extinguishing fluid forcibly impelled into the arcing regions.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawings in which:

Fig. l is an elevational view partly in section of a circuit interrupter embodying the invention and shown in circuit closed position;

Fig. 2 is an enlarged sectional view through one of the interrupting devices shown in Fig. l and embodying the present invention;

Fig. 3 is a cross Ill-lli of Fig. 2;

Fig. 4 is an enlarged cross sectional view taken the line IV-IV of Fig. 2; and

Fig. 5 is a partially enlarged top view of one of the interrupting devices showing the check valves arranged in the housing.

Referring to the drawing by characters of reference, Fig. 1 illustrates an oil circuit breaker unit of the high voltage type such as that used in power transmission systems. Unit 1 is suspended from one line terminal of the circuit interrupter in a suitable tank 2 and submerged in a suitable insulating arc extinguishing fluid, such as oil. A conducting bridging bar 3 serves to connect electrically the arc extinguishing unit 1 with an identical unit 4 in a manner well known in the art. Supported on a cover 5 of the tank 2 are a pair of terminal bushings 6 and 7 (partially shown), to the lower ends of which are secured arc extinguishing units 1 and 4. The cross bar 3 is actuated reciprocally in the vertical direction by an insulating lift rod 8 to open and close the contacts of the are extinguishing units 1 and 4.

Fig. 2 illustrates the internal construction of the arc extinguishing unit 1. Clamped to the lower end of a terminal bushing 6 is a conductive housing 11 which forms a conductive path between it and a movable contact 16. Contact 16 is arranged in a pressure chamber 41 in the closed circuit position, as shown in Fig. 2, the Contact 16 engages a stationary or intermediate contact 13, the latter, in turn,- engaging a lower rod shaped contact 14 sectional view taken along the line along secured to the extremity of the cross bar 3. Contact 14 is arranged in a pressure chamber 42. Contact 13 comprises two contact engaging surfaces. Contact 16 cooperates with one of the contact engaging surfaces to produce a first arc and contact 14 cooperates with the other of the contact engaging surfaces to produce a second arc.

A plurality of rocking finger contacts 15 rest against the upper end of rod shaped contact 16. Current is transferred from housing 11 to contact 16 through rocking finger contacts 15. This arrangement dispenses with braids of similar flexible conductors and also eliminates the necessity of the actuating means for contact 16 for carrying current. In other words, there is a complete and desirable segregation of the current carrying function and the contact operating or actuating function.

In the closed circuit position of the interrupting unit as shown in Figs. 1 and 2, the electric circuit there through comprises the terminal stud (not shown) in bushing 6, housing 11, finger contacts 15, rod contact 16, intermediate contact 13, movable contact 14, conducting cross bar 3, movable contact 14', and the right hand are extinguishing unit 4 as in housing 11 to the terminal stud (not shown) in bushing 7.

Contact 16 is actuated by a pair of levers 17 more clearly shown in Fig. 4 each having an oblong hole 18 in one end thereof and adapted to be rocked about a stud 19. A pin 10 in rod 16 engages oblong hole 18 in each lever 17. Stud 19 which provides rocking support for contact operating levers 17 is supported in and protrudes through the walls 70 of chamber 71. Levers '17 form an integral part of a pair of valve means 72 and 73 which limits the pressure inside of chamber 71 and of the interrupting device 1. The movable valve elements 74 and 75 of valve means 72 and 73 are both coaxially arranged and slidably mounted on stud 19. Each valve element is biased by a pair of helical springs 76 and 77 against the walls of chamber 71 to form a fluid tight seal at the points where the stud 19 and chamber 71 intersect. Valve means 72 and 73 provide an opening in chamber 71 to limit the pressure in chamber 71 of unit 1 if the pressure reaches a predetermined value. A cradle 20 is journaled to levers 17 by means of trunnions 21 and biased downward by a spring 22. Cradle 20 supports a piston stem or rod 23 for the operation of a piston pump 12. Rod 23 guided through a flange 29 stands with its lower extremity in cradle 20 which is arranged to rock freely about the trunnions 21 used to journal levers 17 to cradle 20. Spring 22 is concentrically arranged with rod 23 with one end thereof resting in cradle 20 and the other end thereof against the flange 29. Rod 23 is freely movable about trunnions 21 of cradle 20 and freely movable relative to push rod 25. Cradle 20 is adapted to be operated by an insulating operating tube or rod 25 which in turn is operated by the cross bar 3 of the circuit breaker. When cross bar 3 and operating rod 25 are raised or lowered, the cradle 20 is simultaneously raised or lowered and rocks about pin 21 relative to levers 17 simultaneously with its raising or lowering movement. Means are provided for detachably connecting the push rod to the cradle including plane cooperating surface 80 of the push rod and surface 81 of the cradle 20 to cause the cradle 20 to receive parallel displacement during movement of the cradle while in engagement with the push rod 25. The circuit breaker unit 1 may employ contacts 16 and 13 alone or in combination with spring actuated oil pump 12 for the interruption of line charging currents and such low value of inductive currents as are not effectively interrupted by other types of devices. Oil pump 12 comprising a spring 90 arranged between one end of pump cylinder 26 and piston 24 forces the piston 24 and rod 23 downward during a circuit breaker contact opening operation to force oil in cylinder 26 into the zones of arc initiation. Spring 90 is compressed during a circuit breaker closing operation by the upward movement of push rod 25 and piston rod 23.

A valve disk 27 is loosely mounted on rod 23 and biased against the piston 24 of pump 12'by a spring 28. Spring 28 is disposed between the valve disk 27 and a flange 29 secured to housing 11. The piston 24 is provided with a plurality of apertures 30 which form a passageway for oil flow under certain conditions between the upper and lower portions of the housing through piston 24. The apertures are controlled by disk 27.

Fig. 5 illustrates a pair of check valves 83 and 84 which are arranged in chamber 71 which surrounds the contact actuating mechanism for contact 16. These check valves permit a rapid refill of chamber 71 after an opening contact operation and on upward movement of piston 24. Further, these check valves being normally open vent to tank 2 gas pockets which might form in chamber 71.

During a circuit closing operation of the interrupter, the bridging contact member or bar 3 forces the operating rod 25 upward. Operating rod 25 in its upward movement rotates arcing contact lever 17 counterclockwise to cause contact 16 to engage the contact surfaces of the fixed contact 13. Rod 25 in its upward movement to closed circuit position pushes rod 23 upward against the biasing action of the spring biased piston 24 of pump 12.

The are interrupting unit 1 utilizes two groups of barrier plate assemblies and 36 of suitably shaped insulating plates which form part of the walls of the paths through which the arcs produced by contacts 16, 13 and 14 are drawn.

Each interrupting unit is provided with two parallel cylindrical resistor assemblies 45. The upper end of each resistor assembly is conductively connected to an electrostatic shield 46. Shield 46 is conductively connected to housing 11 which in turn is conductively connected to the lower terminal end of the breaker bushing 6. The lower end of each resistor assembly 45 is conductively connected to the lower electrostatic shield 47. Shield 47 is conductively connected to an arcing electrode comprising a disk like member 48 through a conductive circuit ggmprising bolts 49, plate 50, bolts 51 and ring support The lower end of the arc interrupting blast chamber 42 comprises an insulating nozzle 55 forming a fluid opening 56. The arcing electrode 48 is secured within chamber 42 between the lower end of the barrier plate assembly 36 and the blast opening 56.

When it is desired to open the electric circuit passing through the interrupter, or when overload conditions exist in the electric circuit controlled by the interrupter suitable operating mechanism (not shown) moves the insulating lift rod 8 to result in a downward movement of the conducting cross bar 3 and the movable contacts 14, 14'.

The downward movement of cross bar 3 causes insulating operating rod 25 to rotate lever 17 clockwise about the pivot stud 19 to draw an are between contacts 16 and 13. Substantially simultaneously therewith or with a slight delay the movable contact 14 separates from the intermediate or fixed contact 13 to draw an arc between contacts 13 and 14. The downward movement of operating rod 25 causes the downward movement of piston 24 to move the oil within the pump cylinder 26. The oil, now under pressure within the pump cylinder 26 flows under pressure out of the cylinder 26 through passageway 37, through the barrier plate stack 35 transversely of the longitudinal axis of the arc extinguishing unit 1, through the passageway 38 into chamber 39 and through orifice 4G to the inside of tank 2.

As shown in Fig. 2, an aperture 6% may be provided in plate 61 which separates the upper grid assembly 35 from the chamber 42 and particularly from the lower grid assembly 36. This aperture 69 may be omitted if it is desired to substantially completely isolate the upper chamber 41 from the lower chamber 42.

If aperture is provided in plate 61 then the are drawn between the contacts 16 and 13 may be called a pressure generating arc and the are drawn between contacts 13 and 14 an interrupting arc. With aperture 60 in plate 61, piston 24 causes a first flow of fluid under pressure through the passageway 37, through the passageway 62 extending across the barrier plates of assembly 35. The passageway 62 extending through the barrier plates also extends across the passageway 63 extending through the barrier plates longitudinally of the axis of the interrupter. Piston 24 also causes a second flow of fluid under pressure through passageway 37, aperture 60 in plate 61, chamber 42 and into the barrier plate assembly 36. The first blast of fluid under pressure cools and extinguishes the pressure generating arc and the second blast of fluid under pressure cools and extinguishes the interrupting arc.

During the interruption of low currents, the operating rod 25 moves downwardly at the same speed as the cross bar 3 to result in the lever 17 rotating clockwise about stud 19 to draw an are between contacts 16 and 13. The rod 23 and piston 24 follow the downward movement of operating rod 25. Valve disk 27 closes apertures 30 and moves the oil in cylinder 26 into passageway 37. This action occurs during the interruption of low currents.

During the interruption of high current arcs, the pressure created by the arc drawn between contacts 16 and 13 may prevent the downward movement of the piston 24 and this, in turn, halts the downward movement of the rod 23. The cradle 20 then separates from rod 23.

When the pressure subsides within the barrier plate assembly 35 oil under pressure within housing 26 flows out through barrier plate assembly 35 to flush the region where the arc occurred between contacts 16 and 13. This scavenging action raises the dielectric strength of the oil in the barrier plate assembly 35 and prevents restriking between contacts 16 and 13 which would prolong the arcing time of the interrupter. It also prevents premature breakdown of the contact gap during and immediately following closing operation. The grid assembly 35 is particularly useful in circuit breakers used to isolate a capacitive load of such capacitance and voltage that the voltage gradient across the arc interrupting contacts of the circuit breaker exceeds the dielectric strength between these contacts.

Thus, for efiicient circuit breaker operation it is desirable to provide an arc extinguishing device adjacent the pressure generating are as well as the interrupting arc or adjacent serially connected arcs.

The downward movement of contact 14 draws an arc in the barrier plate stack assembly 36 between contact 14 and the fixed contact 13. The are drawn between contacts 13 and 14 breaks down a portion of the arc extinguishing liquid which surrounds the arc and saturates the barrier plate assembly 36. The barrier plate assembly 36 may be of the type shown and claimed in U. S. Patent No. 2,467,542, P. L. Taylor, April 19, 1949. This type of barrier plate assembly provides helical passages which produce a helical flow of liquid through the barrier plates and the contact passageway 32 formed therein. Most of the disks shown in the barrier plate assembly 36 have three cutout sections 64, which sections are aligned in the stack to form longitudinal venting passages 65. As the contact passageway 32 extends downward through the barrier plate assembly 36, vents 66 arranged in a number of the barrier plates of assembly 36 extend laterally from the contact passageway 32 to the longitudinal venting passages 65 as shown in Fig. 3. Venting passages 65 communicate with a plurality of exhaust ports 67 provided in the insulating shell 63 forming a part of the structure of unit 1.

While the circuit breaker is opening the arcing surface 33 of the movable contact 14 passes the arcing electrode 48 before passing through nozzle 55. Part of contact 14 moves through the nozzle during interruption of the power arc. Immediately after momentary interruption at a current zero the returning voltage between contacts 13 and 14 causes current to flow through the resistor assembly 45 because the voltage breaks down the gap at one or more points on the surface of arcing electrode 48 (due to the short gap between the electrode 48 and the body of contact 14 as compared with the main interrupting gap between surface 33 and contact 13). The resistor assembly 45 is thereby inserted in series with the power circuit through an auxiliary arc so that the resistance circuit now shunts the contacts 14, 16 and 13.

The magnitude or" the arc current is correspondingly decreased by the resistance and the difficulty of completely interrupting the current is greatly diminished, particularly in the case of circuits having high rates of increase of the recovery voltage and also in the case of capacitance switching. The ohmic value of the resistance 45 depends on the characteristics of the circuit to be controlled.

When the comparatively weak arc current through the resistor is finally extinguished by the cooling eifect of the oil, further downward movement of contact 14 serves to increase the oil gap for isolating the contacts from each other so that there is no danger of fiashover or restriking of the arc.

Thus, an efficient, simple and compact interrupting unit is provided that occupies practically no more space within the oil tank than conventional interrupting chambers and that is easy to inspect or repair. The resistor unit can be readily removed from the breaker and replaced independently of the chamber and the contacts therein so that complete disassembly of the chamber construction is unnecessary.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a circuit interrupter, means for establishing and lengthening an arc comprising a lever pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at one end of said lever, means for guiding said movable contact for reciprocal longitudinal motion, a cradle pivotally mounted at the other end of said lever, a cylinder containing an arc extinguishing fluid, a piston arranged in said cylinder, a push rod guided for reciprocal longitudinal motion, means for detachably connecting said push rod to said cradle and to said piston including plane cooperating surfaces of said push rod and of said cradle to cause said cradle to receive a parallel displacement during movement of said cradle in engagement with said push rod, means for biasing said lever, said piston and said cradle in contact open direction, means for actuating said push rod in one direction to move said cradle, said piston and said lever to contact closed position against the biasing action of said biasing means, and means for actuating said push rod in another direction to disconnect said push rod, said cradle and said lever from said piston and to cause said biasing means to move said lever and said cradle in contact opening direction to separate said arcing contacts independently of the movement of said piston and to cause said piston to force fluid under pressure adjacent said arcing contacts to extinguish the arc.

2. In a circuit interrupter, means for establishing and lengthening an arc comprising a lever pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at one end of said lever, means for guiding said movable contact for reciprocal longitudinal motion, a cradle pivotally mounted at the other end of said lever, a cylinder containing an arc extinguishing fluid, a piston arranged in said cylinder, a piston rod attached to said piston, means for detachably connecting said piston rod to said cradle, a push rod guided for reciprocal longitudinal motion,

means for detachably connecting said push rod to said cradle including plane cooperating surfaces of said push rod and of said cradle to cause said cradle to receive a parallel displacement during movement of said cradle in engagement with said push rod, means for biasing said lever, said piston and said cradle in contact open direction, means for actuating said push rod in one direction to move said cradle, said piston and said lever to contact closed position against the biasing action of said biasing means, and means for actuating said push rod in another direction to disconnect said cradle from said piston rod and to cause said biasing means to move said lever and said cradle in contact opening direction to separate said arcing contacts and to cause said piston to force fluid under pressure adjacent said arcing contacts to extinguish the arc.

3. In a circuit breaker: an arc extinguishing device immersed in arc extinguishing fluid, a pressure generating chamber in said device, means for establishing and lengthening an arc in said chamber comprising a sta tionary arcing contact, a movable arcing contact, a stud supported in and protruding through said chamber, a lever pivotally mounted on said stud at a point on said lever between the ends thereof, said movable arcing contact mounted at one end of said lever for reciprocal movement therewith, a push rod, means for connecting said push rod to said lever, means for biasing said lever in contact opening direction, means for actuating said push rod in one direction to rotate said lever to contact closed position against the biasing action of said biasing means, means for actuating said push rod in another direction to cause said biasing means to rotate said lever in contact opening direction to separate said arcing contacts, and valve means mounted on said stud for providing an opening in said chamber to limit the pressure in said chamber if it reaches a predetermined value.

4. In a circuit breaker: an arc extinguishing device immersed in arc extinguishing fluid, a pressure generating chamber in said device, means for establishing and lengthening an arc in said chamber comprising a stationary arcing contact, a movable arcing contact, a stud supported in and protruding through said chamber, a lever pivotally mounted on said stud at a point on said lever between the ends thereof, said movable arcing contact mounted at one end of said lever for reciprocal movement therewith, a push rod, means for detachably connecting said push rod to said lever, means for biasing said lever in contact opening direction, means for actuating said push rod in one direction to rotate said lever to contact closed position against the biasing action of said biasing means, means for actuating said push rod in another direction to cause said biasing means to rotate said lever in contact opening direction to separate said arcing contacts, and valve means comprising a valve element coaxially arranged on one end of said stud outside of said chamber and biased toward said chamber to form a substantially fluid tight seal at the point of intersection of said chamber and said stud, said valve element providing an opening in said chamber to limit the pressure in said chamber if it reaches a predetermined value.

5. in a circuit breaker: an arc extinguishing device immersed in arc extinguishing fluid, a pressure generating chamber in said device, means for establishing and lengthening an arc in said chamber comprising a stationary arcing contact, a movable arcing contact, a stud supported in and protruding through said chamber, a lever pivotally mounted on said stud at a point on said lever between the ends thereof, said movable arcing contact iounted at one end of said lever for reciprocal movement therewith, a cradle pivotally mounted at the other end thereof, a push rod guided for reciprocal longitudinal motion, means for detachably connecting said push rod to said cradle including plane cooperating surfaces of said push rod and of said cradle to cause said cradle to receive parallel displacement during movement of said cradle in engagement with said push rod, means for biasing said lever in contact opening direction, means for actuating said push rod in one direction to actuate said cradle and said lever to contact closed position against the biasing action of said biasing means, means for actuating said push rod in another direction to cause said biasing means to move said lever in contact opening direction to separate said arcing contacts, and valve means mounted on said stud for providing an opening in said chamber to limit the pressure in said chamber if it reaches a predetermined value.

6. In a circuit breaker: an arc extinguishing device immersed in arc extinguishing fluid, a pressure generating chamber in said device, means for establishing and lengthening an arc in said chamber comprising a stationary arcing contact, a movable arcing contact, a stud supported in and protruding through said chamber, a lever pivotally mounted on said stud at a point on said lever between the ends thereof, said movable arcing contact mounted at one end of said lever for reciprocal movement therewith, a cradle pivotally mounted at the other end thereof, a push rod guided for reciprocal longitudinal motion, means for detachably connecting said push rod to said cradle including plane cooperating surfaces of said push rod and of said cradle to cause said cradle to receive parallel displacement during movement of said cradle in engagement with said push rod, means for biasing said lever in contact opening direction, means for actuating said push rod in one direction to actuate said cradle and said lever to contact closed position against the biasing action of said biasing means, means for actuating said push rod in another direction to cause said biasing means to move said lever in contact opening direction to separate said arcing contacts, and valve means comprising a valve element coaxially arranged on one end of said stud outside of said chamber and biased toward said chamber to form a substantially fluid tight seal at the point of intersection of said chamber and said stud, said valve element providing an opening in said chamber to limit the pressure in said chamber if it reaches a predetermined value.

7. In a circuit breaker: an arc extinguishing device immersed in arc extinguishing fluid, a pressure generating chamber in said device, means for establishing and lengthening an arc in said chamber comprising a stationary arcing contact, a movable arcing contact, a stud supported in and protruding through said chamber at two points thereof, a lever pivotally mounted on said stud at a point on said lever between the ends thereof, said movable arcing contact mounted at one end of said lever for reciprocal movement therewith, a cradle pivotally mounted at the other end thereof, a push rod guided for reciprocal longitudinal motion, means for detachably connecting said push rod to said cradle, means for biasing said lever in contact opening direction, means for actuating said push rod in one direction to actuate said cradle and said lever to contact closed position against the biasing action of said biasing means, means for actuating said push rod in another direction to cause said biasing means to move said lever in contact opening direction to separate said arcing contacts, and valve means comprising a pair of valve elements arranged on said stud one at each end thereof outside of said chamber, means arranged on each end of said stud for biasing said valve elements against said chamber to form a substantially fluid tight seal at the points of intersection of said stud and said chamber, said valve elements providing an opening in said chamber to limit the pressure in said chamber if it reaches a predetermined value.

8. in a circuit interrupter, means for establishing and lengthening an arc comprising a lever pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at the other end thereof, a push rod guided for reciprocal longitudinal motion, means comprising plane cooperating surfaces of said push rod and or said cradle for connecting said push rod to said cradle to cause said cradle to receive a parallel displacement during movement of said cradle in engagement with said push rod and for physically separating said push rod from said cradle during a contact opening operation, means for biasing said lever and said cradle in contact open direction, means for actuating said push rod in one direction to actuate said cradle and said lever to contact closed position against the biasing action of said biasing means, and means for actuating said push rod in another direction to cause said biasing means to move said lever and said cradle in contact opening direction to separate said arcing contacts and to separate said push rod from said cradle.

9. In a circuit interrupter, means for establishing and lengthening an arc comprising a lever pivotally mounted at a point between the ends thereof, a pair of arcing contacts comprising a movable contact mounted at one end of said lever, a cradle pivotally mounted at the other end thereof, a cylinder containing an arc extinguishing fluid, a piston arranged in said cylinder, a push rod guided for reciprocal longitudinal motion, means comprising plane cooperating surfaces of said push rod and of said cradle for connecting said push rod to said cradle and to said piston to cause said cradle to receive a parallel displacement during movement of said cradle in engagement With said push rod and for physically separating said push rod from said cradle during a contact opening operation, means for biasing said lever and said cradle in contact open direction, means for actuating said push rod in one direction to move said cradle, said piston and said lever to contact closed position against the biasing action of said biasing means, and means for actuating said push rod in another direction to physically separate said push rod, said cradle and said lever from said piston and to cause said biasing means to move said lever and said cradle in contact opening direction to separate said arcing contacts and to cause said piston to force fluid under pressure adjacent said arcing contacts to extinguish the arc.

References Cited in the file of this patent UNITED STATES PATENTS 2,445,442 Leeds et al. July 20, 1948 2,606,262 Bartlett Aug. 5, 1952 2,619,568 Leeds Nov. 25, 1952 2,621,273 Friedrich et al. Dec. 9, 1952 2,695,349 Baker Nov. 23, 1954 

